Research and development of holographic memories have been advanced as large-capacity recording technique making high-speed transmission possible. O plus E, vol. 25, No. 4, 385-390 (2003) describes basic structures of holographic memories and a coming prospect thereof.
Examples of the property required for a hologram recording material include high refractive index change at the time of recording, high sensitivity, low scattering, environment resistance, durability, low dimensional change, and high multiplicity. As a hologram recording material, there is known a photopolymer material made mainly of an organic binder polymer and a photopolymerizable monomer.
For example, JP-A-11-512847 discloses a volume hologram recording medium comprising an acid generator capable of generating an acid when the generator is exposed to chemical ray radiation; a binder; and at least one monomer or oligomer capable of undergoing cationic polymerization which is initiated with the acid generated from the acid generator. As the binder, a siloxane polymer or oligomer, or an acrylate is disclosed.
JP-A-8-101627 discloses a photosensitive composition for volume hologram recording, comprising (a) a glycidyl group-containing compound wherein the remaining chlorine content by percentage is 1% or less by weight, (b) a radical polymerizable compound, (c) a radical photopolymerization initiator which is sensitized to a laser beam or a light good in coherency to polymerize the component (b), and (d) a cationic polymerization initiator.
The hologram recording materials described in the both publications are each in a liquid form and are required to be subjected to pre-exposure treatment at time of hologram recording; at the initial stage of exposure, recording cannot be attained. In other words, when each of the recording materials is in a liquid phase so as to have fluidity, interference bands generated by light interference are not kept in the position thereof; therefore, it is necessary to subject the material to exposure treatment in advance to decrease the fluidity. Additionally, when the hologram recording material is in a liquid form, there is caused a problem that after the formation of a recording medium the recording material leaks out from the medium.